Glass fiber is an inorganic fiber material and can be used to reinforce resins to produce composite materials with good performance. As a reinforcing base material for advanced composite materials, high-performance glass fibers were originally used mainly in the aerospace industry or the national defense industry. With the progress of science and technology and the development of economy, high-performance glass fibers have been widely used in civil and industrial fields such as motors, wind blades, pressure vessels, offshore oil pipes, sports apparatus and auto industry.
Since the American company developed S-2 glass fiber, different countries have developed high-performance glass fibers with various compositions, e.g. R glass fiber developed by a French company, HiPer-tex glass fiber developed by an American company and high-strength glass fiber #2 developed by a Chinese company. The original high-performance glass compositions were based on an MgO—Al2O3—SiO2 system and a typical solution was S-2 glass of an American company. However, the production of S-2 glass is excessively difficult, as its forming temperature is up to about 1571° C. and its liquidus temperature up to 1470° C. and therefore it is difficult to realize large-scale industrial production.
Thereafter, in order to decrease the melting temperature and forming temperature of glass to better satisfy the needs of large-scale production with refractory-lined furnaces, large companies successively developed high-performance glasses based on an MgO—CaO—Al2O3—SiO2 system. Typical solutions were R glass of French company and HiPer-tex glass of American company, which were a trade-off for production scale by sacrificing some of the glass properties. However, as these designed solutions were too conservative, especially the content of Al2O3 was kept more than 20%, preferably 25%, the production of glass remained highly difficult. Although small-scale production with refractory-lined furnace was achieved, the production efficiency was low and the cost performance ratio of the products was not high. The traditional R glass is difficult to fiberized as its forming temperature is up to about 1410° C. and its liquidus temperature up to 1330° C., which causes difficulty in attenuating glass fiber and consequently in realizing large-scale industrial production.
In addition, there is another type of R glass, of which the mechanical properties are slightly lower than those of the traditional R glass and its melting and forming properties are significantly superior to those of the traditional R glass. However, as its ratio of calcium to magnesium is quite high. The glass has a high risk for crystallization (devitrification). In addition, since too much Li2O is introduced, not only the chemical stability of the glass is affected, but also its raw material cost is higher. Therefore it is also not suitable for large-scale industrial production.
The High-strength 2# glass fiber mainly comprises SiO2, Al2O3 and MgO, and certain amounts of Li2O, B2O3, CeO2 and Fe2O3 are also introduced. It also has high strength and high modulus and its forming temperature is only about 1245° C. and its liquidus temperature is 1320° C. Both temperatures are much lower than those of S glass fiber. However, since its forming temperature is lower than its liquidus temperature, which is unfavorable for the control of glass fiber attenuation. Its forming temperature has to be increased and specially-shaped tips have to be used to prevent a glass crystallization phenomenon from occurring in the fiber attenuation process. This causes difficulty in temperature control and also makes it difficult to realize large-scale industrial production.
To sum up, we find that, at present stage, in the actual production of various high-performance glass fibers lies a common issue which is that the liquidus temperature of glass is too high and the crystallization risk is great, At present, the liquidus temperature of the mainstream E glass is generally lower than 1200° C., while the liquidus temperature of above-mentioned high-performance glasses is generally higher than 1300° C., which will cause the glass crystallization phenomenon to occur easily during the production process. As a result, the production efficiency of glass fibers and the service life of refractory materials and platinum bushings are greatly reduced.